Assessment of long-term energy efficiency improvement and greenhouse gas emissions mitigation options for the cement industry

Highlights

• A bottom-up and technology-rich model is developed for the cement industry.

• Energy consumption demand tree is used to analyze the energy intense sub-processes.

• 20 scenarios are developed to assess the long-term energy saving and GHG mitigation.

• Carbon abatement cost curves are developed to rank energy saving options.

Abstract

The cement industry is responsible for between 5% and 9% of global greenhouse gas (GHG) emissions. The increasing trend of GHG emissions from cement sector highlights the importance of GHG mitigation in this industry. In the current study, bottom-up energy modelling and scenario analyses were used to assess long-term GHG mitigation potential in the cement industry. The developed comprehensive, data-intensive, and technology-rich model is flexible and can be used to study the GHG mitigation potential in different regions. For the case study of Canada, a reference scenario along with 20 GHG emissions' reduction scenarios were developed in the Long-range Energy Alternative Planning (LEAP) model. For each scenario, cumulative energy saving and GHG reduction potential were analyzed. Furthermore, the net present value, cost of saved energy, and carbon were calculated to assess the economic performance of different scenarios. Carbon abatement cost curves were also developed using the GHG mitigation potential and the cost of implementing different energy efficiency options. Overall, compared to the reference scenario, the cumulative GHG mitigation potentials in the Canadian cement sector are 27 and 59 million tonnes CO₂eq. by the years 2030 and 2050, respectively. More than 70% of the emissions’ reduction is achievable with negative cost.

Introduction

Historically, the cement sector has been responsible for between 5% [1] and 9% [2] of global greenhouse gas (GHG) emissions. In 2010, more than 2800 million tonnes of GHGs were emitted from the industry, a figure corresponding to 9% of global CO₂ emissions [1]. In addition, the fast growth rate of the industry (more than 200% increase between 2003 and 2015) [3] highlights the increasing role of the cement industry in global CO₂ emissions; and emphasizes the importance of GHG mitigation in this sector.

In the cement industry, CO₂ is generated not only through fuel combustion but also as an inherent part of the process (i.e., calcination) [4]. More specifically, unlike most of the manufacturing sector, where the GHG emissions are mainly a result of energy consumption, in the cement production industry, both energy consumption and the cement production process itself lead to CO₂ emissions. In Canada, process- and energy-related CO₂ emissions account for 52% and 48% of the overall emissions from the cement industry [4].

Process-related emissions are generated in the calcination process (CaCO3→ CaO + CO2), where 0.5 kg of CO₂ is produced for each kilogram of clinker. The specific process-related CO₂ emissions are between 0.5 and 0.95 kg CO₂/kg cement depending on the clinker ratio [4]. These emissions cannot be mitigated through energy efficiency improvement or fuel switching.

The energy-induced emissions from the cement industry are either direct or indirect. Direct fuel-related emissions result from fuel combustion on the production site, and indirect emissions are generated as a result of electricity consumption. Depending on the source of emissions, there are various GHG mitigation strategies in the cement industries, i.e., process modification, energy efficiency improvement, and the use of alternative fuels [5].

The applicability of the GHG mitigation options in the cement industry is subject to several factors including technological and economic performance as well as the effectiveness of the options in reducing GHG emissions. In order to assess the energy savings and GHG mitigation potential in the cement industry, detailed technology assessment has been proved to be effective tool [4]. Scenario analyses are also used in some studies to investigate the performance of the cement industry on national [6], regional [7] and global [8] levels. While these studies mainly focus on the long-term applicability of different options and analyze the achievable mitigation potential through implementing the options, other studies assess the economic performance of the energy efficiency technologies through various economic indicators. In a European-wide study, for instance, different techniques such as payback period, net present value, and internal rate of return were used to analyze the economic feasibility of energy efficiency improvement in the cement industry [9]. Similar studies have been done in China [10] and the United States [11], where economic factors together with the performance indicator of technologies (i.e., energy savings potential) are used to analyze the cost of saved energy and develop conservation supply curves. Madlool et al. [12] reviewed the global status of the cement industry in terms of energy use and energy saving potential. They also analyzed various energy saving options, their GHG mitigation potential (calculated based on the reduction in energy consumption), and the economic performance (calculated for some of the options where calculations were based on the energy saving alone).

Analyzing the existing literature reveals that despite the important role that cement industry could play in the global GHG mitigation, the long-term system-level evolution of the industry and the role that energy efficiency improvement can play in mitigating GHG emissions from the sector is less understood. In other words, comprehensive literature review reveals that the most common methods for analyzing the industrial energy efficiency improvement are techno-economic assessment and policy analysis. More specifically, while in the first group of studies techno-economic assessment techniques are used to assess the feasibility of various GHG mitigation options in iron and steel [13] and chemical industries [14], the latter category of studies applies a high level perspective to assess the energy efficiency improvement potential at system level (with less emphasize on the technological performance of individual processes) [15].

Application of bottom-up energy modelling and scenario analysis could help bridging the gap between technology-specific energy efficiency analysis and system-wide GHG mitigation assessment (while considering the development of the energy system at different levels). Although the bottom-up energy modelling techniques has been widely used to study the long-term development of the sectors such as electricity generation [16], residential [17], transportation sector [18] etc., complexity of the industrial sector, the long life-time of the technologies in the sector and the role of energy carriers both as a source of energy and in some industries [19] as a feedstock has imposed limitations on application of the method in industrial sector energy efficiency analysis.

Therefore, the primary objective of the current study is to develop a detailed and technology-rich bottom-up energy modelling framework (including both energy supply and demand sides) to assess the technologically feasible GHG mitiation potential while accounting for the intractions between the energy supply and demand sectors at the system level. This helps, analyzing the actual emissions mitigation potential (a combination of direct mitigation at the demand point and indirect mitigation as a result of electricity consumption). In addition, different economic indicators (namely cost of saved energy and cost of saved carbon) are calculated to assess the economic performance of different GHG mitigation efforts.

The proposed framework is applicable for analyzing the current status of the system by identifying the major energy consumers (at process and technology level) and assessing the applicable energy efficiency measures and their adoption potential. This provides the ground to develop long-term mitigation scenario to evaluate the GHG mitigation potential and its associated cost.

The detailed and technology-rich framework is flexible and could be easily transferred in the scientific community to study the long-term GHG mitigation potential from the cement industry in other jurisdictions. In addition, given the considerable share of the energy in the overall cost of industry, share of cement industry in the global GHG emissions and the existing and emerging regulations around carbon emissions at both national and global levels, the results of the analysis are expected to provide invaluable input to both industrial stakeholders and policy makers for the long-term climate mitigation strategy development.